1. Chapter 12 Solutions

2. Colligative Properties
colligative properties are properties whose value depends only on the number of solute particles, and not on what they are
Vapor Pressure Depression, Freezing Point Depression, Boiling Point Elevation, Osmotic Pressure
Solutions of ionic substances often have a vapor pressure significantly lower than predicted, because the ion-dipole forces between the dissolved ions and polar water molecules are so strong.

3. the van’t Hoff factor, i, is the ratio of moles of solute particles to moles of formula units dissolved
measured van’t Hoff factors are often lower than you might expect due to ion pairing in solution

4. Ionic Solutes and Vapor Pressure
according to Raoult’s Law, the effect of solute on the vapor pressure simply depends on the number of solute particles
when ionic compounds dissolve in water, they dissociate – so the number of solute particles is a multiple of the number of moles of formula units
the effect of ionic compounds on the vapor pressure of water is magnified by the dissociation
since NaCl dissociates into 2 ions, Na+ and Cl, one mole of NaCl lowers the vapor pressure of water twice as much as 1 mole of C12H22O11 molecules would

5. Example –
What is the vapor pressure of H2O when mol MgCl2 is mixed with mol 55°C?

7. Freezing Point Depression
the freezing point of a solution is lower than the freezing point of the pure solvent
for a nonvolatile solute
therefore the melting point of the solid solution is lower
the difference between the freezing point of the solution and freezing point of the pure solvent is directly proportional to the molal concentration of solute particles
(FPsolvent – FPsolution) = DTf = m • Kf • i
the proportionality constant is called the Freezing Point Depression Constant, Kf
the value of Kf depends on the solvent
the units of Kf are °C/m

8. Boiling Point Elevation
the boiling point of a solution is higher than the boiling point of the pure solvent
for a nonvolatile solute
the difference between the boiling point of the solution and boiling point of the pure solvent is directly proportional to the molal concentration of solute particles
(BPsolution – BPsolvent) = DTb = m • Kb • i
the proportionality constant is called the Boiling Point Elevation Constant, Kb
the value of Kb depends on the solvent
the units of Kb are °C/m

9. Kf

10. Example
What is the normal boiling point in oC of an antifreeze solution prepared by dissolving g of ethylene glycol (C2H6O2) in g of water? The molal boiling point elevation constant for water is 0.51 oC•kg/mol and molar mass of ethylene glycol is g/mol

11. Ex 12. 9 – How many g of ethylene glycol, C2H6O2, must be added to 1
Ex 12.9 – How many g of ethylene glycol, C2H6O2, must be added to 1.0 kg H2O to give a solution that boils at 105°C?

12. Example
Calculate the freezing point of an aqueous 0.10 m FeCl3 solution using a van’t Hoff factor of 3.2.

13. Example
Calculate the freezing point of an aqueous m FeCl3 solution if all FeCl3 completely ionized
Tro, Chemistry: A Molecular Approach

14. PROPERTIES OF SOLUTIONS
contain small particles (ions or molecules).
are transparent.
do not separate.
cannot be filtered.
Suspensions
have very large particles.
settle out.
can be filtered.
must be stirred to stay suspended.
Examples include: blood platelets, muddy water, and calamine lotion.

15. Colloids
a colloidal suspension is a heterogeneous mixture in which one substance is dispersed through another
most colloids are made of finely divided particles suspended in a medium
the difference between colloids and regular suspensions is generally particle size – colloidal particles are from 1 to 100 nm in size
the particles in a colloid exhibit Brownian motion
colloids exhibit the Tyndall Effect
scattering of light as it passes through a suspension
colloids scatter short wavelength (blue) light more effectively than long wavelength (red) light

16. Colloids
a colloidal suspension is a heterogeneous mixture in which one substance is dispersed through another
most colloids are made of finely divided particles suspended in a medium
the difference between colloids and regular suspensions is generally particle size – colloidal particles are from 1 to 100 nm in size

17. Solutions, Colloids, and Suspensions
Copyright © by Pearson Education, Inc.

18. Osmosis
osmosis is the flow of solvent through a semi-permeable membrane from solution of low concentration to solution of high concentration
the amount of pressure needed to keep osmotic flow from taking place is called the osmotic pressure
the osmotic pressure, P, is directly proportional to the molarity of the solute particles
R = (atm∙L)/(mol∙K)
P = MRT

19. Suppose a semipermeable membrane separates a 4% starch solution from a 10% starch solution. Starch is a colloid and cannot pass through the membrane, but water can. What happens?
4% starch
10% starch
H2O

20. Ex 12. 10 – What is the molar mass of a protein if 5. 87 mg per 10
Ex – What is the molar mass of a protein if 5.87 mg per 10.0 mL gives an osmotic pressure of 2.45 torr at 25°C?

21. ISOTONIC SOLUTIONS An isotonic solution
exerts the same osmotic pressure as red blood cells.
is known as a “physiological solution.”
of 5.0% glucose or 0.90% NaCl is used medically because each has a solute concentration equal to the osmotic pressure equal to red blood cells.
H2O

22. HYPOTONIC SOLUTIONS H2O A hypotonic solution
has a lower osmotic pressure than red blood cells.
has a lower concentration than physiological solutions.
causes water to flow into red blood cells.
causes hemolysis: RBCs swell and may burst.
H2O

23. HYPERTONIC SOLUTIONS A hypertonic solution
has a higher osmotic pressure than RBCs.
has a higher concentration than physiological solutions.
causes water to flow out of RBCs.
cause crenation: RBCs shrink in size.
H2O